Paroxysmal nocturnal hemoglobinuria (PNH) is a hematopoietic stem cell disorder in which unregulated activation of the complement system leads to significant ischemic morbidities with shortened lifespan. Life-threatening thromboembolism (TE) is the most feared complication of PNH, accounting for up to 45% of patient deaths. It is estimated that 40% of PNH patients experience a clinically evident TE and 60% of patients without clinically diagnosed TE demonstrate TE by high-sensitivity MRI, indicating the ongoing thrombotic risk in most patients with PNH. Much of these data come from PNH patients from European descent. To understand the impact of TE in patients with PNH from non-European regions, we performed this study to evaluate the clinical characteristics of Korean patients with PNH.